CA1236265A - .alpha. ALUMINA PRODUCTION IN A STEAM-FLUIDIZED REACTOR - Google Patents
.alpha. ALUMINA PRODUCTION IN A STEAM-FLUIDIZED REACTORInfo
- Publication number
- CA1236265A CA1236265A CA000496908A CA496908A CA1236265A CA 1236265 A CA1236265 A CA 1236265A CA 000496908 A CA000496908 A CA 000496908A CA 496908 A CA496908 A CA 496908A CA 1236265 A CA1236265 A CA 1236265A
- Authority
- CA
- Canada
- Prior art keywords
- alumina
- product
- temperature
- reactor
- maintained
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
- C01F7/00—Compounds of aluminium
- C01F7/02—Aluminium oxide; Aluminium hydroxide; Aluminates
- C01F7/44—Dehydration of aluminium oxide or hydroxide, i.e. all conversions of one form into another involving a loss of water
- C01F7/441—Dehydration of aluminium oxide or hydroxide, i.e. all conversions of one form into another involving a loss of water by calcination
- C01F7/445—Dehydration of aluminium oxide or hydroxide, i.e. all conversions of one form into another involving a loss of water by calcination making use of a fluidised bed
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2006/00—Physical properties of inorganic compounds
- C01P2006/12—Surface area
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10S423/00—Chemistry of inorganic compounds
- Y10S423/09—Reaction techniques
- Y10S423/16—Fluidization
Abstract
Abstract of the Disclosure A process for transforming alumina hydrate into an anhydrous product comprising at least 10 wt% alpha alumina.
Alumina hydrate is dehydrated, heated and transferred to a reactor where it is fluidized with steam and maintained at a temperature of about 900-1350°C. Steam fluidization enhances crystal growth and results in a product having uniform quality and superior grinding characteristics.
Alumina hydrate is dehydrated, heated and transferred to a reactor where it is fluidized with steam and maintained at a temperature of about 900-1350°C. Steam fluidization enhances crystal growth and results in a product having uniform quality and superior grinding characteristics.
Description
26~
The present invention relates to a process involving calcination of alumina in a fluidized bed reactor. The product comprises alpha alumina and is a useful ceramic or refractory material.
Processes for making alpha alumina are known in the prior art. The following articles describe the principles of one such process that is closely related to the present invention: William M. Fish, "Alumina Calcination in the Fluid-Flash Calciner", Light Metals 1974, pages 673-6~2 and Edward W. Lussky, "Experience with Operation of the Alcoa Fluid Flash Calciner", Light Metals 1980, pages 69-79.
Other processes for making products comprising alpha alumina are described in the following patents: Noisome U.S.
Patent No. 2,642,337; Turin U.S. Patent No. 3,265,465; Doyle et at U.S. Patent No. 3,336,109; Hrishikesan U.S. Patent No. 3,4~l2,606; Rev U.S. Patent Jo. 3,565,~08 and Potter U.S.
Patent No. 4,224,288. However, each of these prior art processes suffers from one or more serious limitations making it less than entirely suitable for its intended purpose.
Currently, rotary kiln calcination is the principal method used commercially to produce alumina with a high alpha content. Rotary kiln calcination overcomes a stickiness and agglomeration effect that occurs in high temperature (above about 1220~C) fluidized beds of alumina. This stickiness effect, Imtil now, has prevented the use of fluidized beds for I
I
t `,`
the continuous production of alumina with alpha content greater than about 65 White.
It is a principal object of the present invention to provide a process for transforming alumina hydrate into an an hydrous alumina product comprising alpha alumina wherein transformation to alpha alumina takes place in a reactor containing a Ted that is fluidized with steam.
A related object of the invention is to provide a process for making alpha alumina in a fluidized bed at temperatures which may be greater than 1220C, while avoiding the stickiness effect that has heretofore prevented operation at such temperatures.
It is an advantage of the invention that the process will yield alpha alumina without addition of aluminum trifluoride or other mineralizing agent at an intermediate step.
The alpha alumina product will not, therefore, be contaminated with residual fluoride or other mineralizing agent. Fluoride is known to be detrimental for high strength ceramic applications because it promotes crystal growth during sistering.
Another advantage of the invention is that it saves heat energy compared with prior art alumina calcination processes. Energy usage resulting from practice of the present invention is estimated at about 10-30% less than for rotary kiln calcination.
An additional advantage of the invention is that the alumina produced is more uniformly calcined than with rotary kiln calcination.
3~;26~
A further advantage of the invention is that the process does not require increased pressures and accordingly can be retrofitted to existing fluid flash calcination systems.
Additional objects and advantages of the present invention will become apparent to persons skilled in the art from the following specification and drawings.
In accordance with the present invention, alumina hydrate is transformed into an an hydrous alumina product comprising at least about 10 wit% alpha alumina.
lo The alumina hydrate is initially heated in a dehydrating zone to a sufficiently high temperature and for sufficient time to obtain alumina having a residual water content below about 15 wit%. The alumina is preferably heated to an elevated temperature above about 800C so that residual water content is reduced below about lo wit% and typically is about 5 wit%.
The alumina is transferred into a heating zone and there heated to an elevated temperature greater than the temperature reached by the alumina in the dehydrating zone. The heating zone is preferably located in a furnace heated by combustion of natural gas at a flame temperature of about 1649-1677C. Residence time in the furnace is usually short (about 10 to 100 seconds).
The alumina is next transferred into a reactor separate from the heating zone and there maintained in a fluidized bed at a temperature above about 900C for a sufficient time to transform the alumina into an an hydrous product comprising at least about 10 wit% alpha alumina. A
preferred temperature range is about 900-1350C. Reactor temperature is preferably above about 1100C, more preferably above about 1220C. Residence time varies from about 1 to 45 minutes, depending upon the temperature. Two particularly preferred reactor temperatures are 1250C and 1275C, Reactor pressure is generally below about 1.5 atmospheres (gauge).
The reactor is fluidized with a fluidizing gas comprising principally steam. The flooding gas preferably comprises at least 90 volume percent steam and is usually substantially all (greater than about go volume percent) steam lo An advantage of the present invention is that the steam-fluidized bed can be maintained at about 1220-1300C for long periods of time without losing control over temperature or obtaining excessively sticky particles in the product.
The alumina is heated in the reactor for a sufficient time to obtain an an hydrous product comprising at least about 10 wit% alpha alumina. More preferably, the alpha alumina content is at least about 65 wit%, usually a least about 80 wit%.
The product may have less than about lo mug surface area, generally less than about 6 mug and sometimes less than about 3 mug The hot alumina product is discharged from the reactor into a series of cyclones where it is partially cooled. Final cooling is accomplished in a two-bed heat exchanger comprising an upper air-cooled bed and a lower water-cooled bed.
Figure 1 is a flow sheet diagram of a preferred system for carrying out the process of the present invention.
Figure 2 is an electron microphotograph of an an hydrous alumina product made in accordance with the present invention.
A preferred fluid flash calcination system for carrying out the process of the invention is shown schematically in Figure 1.
alumina hydrate 8 from the Bayer process is filtered and washed with wash water 9 on a conventional table filter 10.
The filtered alumina hydrate at this stage comprises aluminum hydroxide, Allah. The filter product has both free moisture, to the extent of about 8-16 wit% HO, and chemically bound water amounting to about 34.6 wit% on dry Allah. As used herein, the term "residual water content" refers to the sum of free moisture and chemically bound water. For example, alumina containing 34.6 wit% chemically bound water and about 10 wit% free moisture has a residual water content of about 44.6 wit%.
The damp hydrate its fed into a flash dryer 20 through a feed screw 21. A gas line 22 feeds a hot gas stream into the dryer 20$ where tree water is driven off from the alumina hydrate. The dried hydrate is transferred to a first cyclone 30 where it is separated from hot gases and water vapor and discharged into a fluidized bed dryer 40. Hot gases and water vapor from the cyclone 30 are carried to an electrostatic precipitator 42 where dust is removed to a dust bin 43 and a clean off-gas is released to the atmosphere through a vent 44.
The dryer 40 contains alumina that is fluidized by air from an air source 46. The flash dryer 20, cyclone 30 and fluidized bed dryer 40 define, in combination, a dehydrating zone wherein the hydrate is heated to reduce its residual water content. ~eatecl alumina hydrate metered out of the dryer 40 through a valve 47 has a residual water content below about 15 wit%, usually below about 10 wit% and typically about 5 wit%. Off-gas released through the vent 40 contains steam originating from dehydration and calcination of the alumina as well as from steam used as a 1uidizlng gas.
The valve 47 releases hydrate at a controlled rate into a reactor or holding vessel 50. The reactor 50 includes a cyclone portion 51 and a lower portion 52 containing a fluidized bed of alumina. A steam source 53 fluidizes alumina in the reactor 50.
Hydrate released into the cyclone portion 51 contacts a hot gas stream which partially calcites the hydrate and carries it to a second cyclone 60. There, solids are separated from the hot gas and transferred into a furnace 70. Hot gas separated from the solids in the second cyclone 60 may conveniently be returned through a gas line 22 into the flash dryer 20.
In the furnace 70, fuel is burned in a series of peripherally located burners directly into a heating zone 71 containing a suspension of alumina. Residence time in the furnace 70 is short (about 10-100 seconds). The furnace 70 is preferably heated by combustion of natural gas at a flame temperature of about 16~9-1677C (3000-3500F). The furnace 70 may also be heated by combustion of other fossil fuels or by electric heater means. The furnace 70 heats alumina in the heating zone 71 to an elevated temperature above about 800C.
An alumina-gas suspension passes from the furnace 70 into the cyclone portion 51 of the reactor 50. Solid alumina particles separated in the cyclone portion 51 drop downwardly into the 1uidized bed in the lower portion 52.
Lo The fluidized bed is maintained at a temperature above about 900C, usually above about Luke, and preferably above about 1220C. An advantage of the present invention is the ability Jo maintain temperatures above about 1220C in the fluidized bed without losing control over temperature. Two particularly preferred operating temperatures in the reactor 50 are 1250C and 1275C.
A further advantage of the invention is that the reactor 50 does not require increased pressure. Reactor pressure is less than about 1.5 atmospheres, usually about atmospheric pressure or slightly higher.
Alumina is maintained in the fluidized bed reactor 50 for a sufficient time to transform it into an an hydrous alumina product comprising at least about 10 wit% alpha alumina.
Residence time in the reactor may be about 1 to 45 minutes, depending upon the temperature and desired alpha alumina content of the product. The reaction is usually maintained for a sufficient time to raise alpha alumina content to at least about 65 wit%, preferably at least about 80 wit%. The product may have surface area of less than about 10 mug usually less than about 5 mug or even less than about 3 mug Characteristics of the product can be controlled by varying retention time or reaction temperature.
The fl~lidizing gas introduced through the source 53 is principally steam. The fluidizing gas preferably comprises at least about 90 volume percent steam, and is optimally substantially all (greater than about 99 volume percent) s-team.
Usage of steam as the fluldizing gas permits operation of the reactor 50 at higher temperatures than might otherwise be s maintained for long periods of time and avoids collapse of the fluidized bed as a result of alumina particle stickiness at such temperatures. The steam may be superheated to a temperature above about 105C, usually not more than about 200C. The steam promotes crystal growth and enhances conversion to alpha alumina.
The exothermic reaction forming alpha alumina releases heat at a rate of about 133 BTU's per pound of alpha alumina formed. This heat of formation maintains alumina in the fluidized bed at an elevated operating temperature.
Hot alumina product is discharged through a valve Al and pneumatically conveyed through a series of cyclones I where the product is partially cooled. An air pump 81 supplies external air to the cyclones 80. Heated air may be returned from the cyclones 80 through an air duct 82 to the furnace 70 where such heated air provides a major portion of the air required for combustion. A small auxiliary burner 83 adjacent the air duct 82 ensures proper air temperature for combustion and also provides initial heating on start-up.
Alumina is discharged from the cyclones 80 into a two-bed fluidized cooler 90. The alumina is initially cooled with an air-cooled tubular heat exchanger 91 surrounding an upper bed. Air heated here can be transferred to the air source 46 for the fluidized bed dryer 40. Alumina cooled in the upper bed is dropped into a lower bed -for final cooling by a water-cooled heat exchanger 92. An air header 93 supplies air for fluidizing both beds in the cooler 90. The cooled alumina is shifted into a pneumatic conveyor 100 powered by an air source lo and then dumped into an alumina storage bin 110.
~3~6~ii Examples The preferred process described above results in an an hydrous alumina product having high alpha alumina content. A
typical product is shown in Figure 2, which is an electron microphotograph taken at OX magnification. This product was made by treating alumina with steam in the reactor 50 at a temperature of about 1275C. Alpha alumina content is about 85~, based upon intensity as measured by X-ray diffraction.
Surface area (BET) is about 2 mug The product is useful in ceramic and refractory applications calling for alumina having high alpha content. The product has superior grinding characteristics and is more uniform than alpha alumina products produced in a rotary kin.
Alumina heated at 1225C for 30 minutes in a vessel 50 containing a bed fluidized with steam resulted in a product having an alpha alumina content of about 87% and BET surface area of about 4 m go Alumina heated at 1270C for 13 minutes in a vessel 50 containing a bed flooded with steam resulted in a product with an alpha alumina content of about 88% and JET surface area of about 5 mug Various modifications may be made in the invention without departing from the spirit thereof, or the scope of the claims, and therefore, the exact form shown is to be taken as illustrative only and not in a limiting sense, and it is desired that only such limitations shall be placed thereon as are imposed by the prior art, or are specifically set forth in the appended claims.
The present invention relates to a process involving calcination of alumina in a fluidized bed reactor. The product comprises alpha alumina and is a useful ceramic or refractory material.
Processes for making alpha alumina are known in the prior art. The following articles describe the principles of one such process that is closely related to the present invention: William M. Fish, "Alumina Calcination in the Fluid-Flash Calciner", Light Metals 1974, pages 673-6~2 and Edward W. Lussky, "Experience with Operation of the Alcoa Fluid Flash Calciner", Light Metals 1980, pages 69-79.
Other processes for making products comprising alpha alumina are described in the following patents: Noisome U.S.
Patent No. 2,642,337; Turin U.S. Patent No. 3,265,465; Doyle et at U.S. Patent No. 3,336,109; Hrishikesan U.S. Patent No. 3,4~l2,606; Rev U.S. Patent Jo. 3,565,~08 and Potter U.S.
Patent No. 4,224,288. However, each of these prior art processes suffers from one or more serious limitations making it less than entirely suitable for its intended purpose.
Currently, rotary kiln calcination is the principal method used commercially to produce alumina with a high alpha content. Rotary kiln calcination overcomes a stickiness and agglomeration effect that occurs in high temperature (above about 1220~C) fluidized beds of alumina. This stickiness effect, Imtil now, has prevented the use of fluidized beds for I
I
t `,`
the continuous production of alumina with alpha content greater than about 65 White.
It is a principal object of the present invention to provide a process for transforming alumina hydrate into an an hydrous alumina product comprising alpha alumina wherein transformation to alpha alumina takes place in a reactor containing a Ted that is fluidized with steam.
A related object of the invention is to provide a process for making alpha alumina in a fluidized bed at temperatures which may be greater than 1220C, while avoiding the stickiness effect that has heretofore prevented operation at such temperatures.
It is an advantage of the invention that the process will yield alpha alumina without addition of aluminum trifluoride or other mineralizing agent at an intermediate step.
The alpha alumina product will not, therefore, be contaminated with residual fluoride or other mineralizing agent. Fluoride is known to be detrimental for high strength ceramic applications because it promotes crystal growth during sistering.
Another advantage of the invention is that it saves heat energy compared with prior art alumina calcination processes. Energy usage resulting from practice of the present invention is estimated at about 10-30% less than for rotary kiln calcination.
An additional advantage of the invention is that the alumina produced is more uniformly calcined than with rotary kiln calcination.
3~;26~
A further advantage of the invention is that the process does not require increased pressures and accordingly can be retrofitted to existing fluid flash calcination systems.
Additional objects and advantages of the present invention will become apparent to persons skilled in the art from the following specification and drawings.
In accordance with the present invention, alumina hydrate is transformed into an an hydrous alumina product comprising at least about 10 wit% alpha alumina.
lo The alumina hydrate is initially heated in a dehydrating zone to a sufficiently high temperature and for sufficient time to obtain alumina having a residual water content below about 15 wit%. The alumina is preferably heated to an elevated temperature above about 800C so that residual water content is reduced below about lo wit% and typically is about 5 wit%.
The alumina is transferred into a heating zone and there heated to an elevated temperature greater than the temperature reached by the alumina in the dehydrating zone. The heating zone is preferably located in a furnace heated by combustion of natural gas at a flame temperature of about 1649-1677C. Residence time in the furnace is usually short (about 10 to 100 seconds).
The alumina is next transferred into a reactor separate from the heating zone and there maintained in a fluidized bed at a temperature above about 900C for a sufficient time to transform the alumina into an an hydrous product comprising at least about 10 wit% alpha alumina. A
preferred temperature range is about 900-1350C. Reactor temperature is preferably above about 1100C, more preferably above about 1220C. Residence time varies from about 1 to 45 minutes, depending upon the temperature. Two particularly preferred reactor temperatures are 1250C and 1275C, Reactor pressure is generally below about 1.5 atmospheres (gauge).
The reactor is fluidized with a fluidizing gas comprising principally steam. The flooding gas preferably comprises at least 90 volume percent steam and is usually substantially all (greater than about go volume percent) steam lo An advantage of the present invention is that the steam-fluidized bed can be maintained at about 1220-1300C for long periods of time without losing control over temperature or obtaining excessively sticky particles in the product.
The alumina is heated in the reactor for a sufficient time to obtain an an hydrous product comprising at least about 10 wit% alpha alumina. More preferably, the alpha alumina content is at least about 65 wit%, usually a least about 80 wit%.
The product may have less than about lo mug surface area, generally less than about 6 mug and sometimes less than about 3 mug The hot alumina product is discharged from the reactor into a series of cyclones where it is partially cooled. Final cooling is accomplished in a two-bed heat exchanger comprising an upper air-cooled bed and a lower water-cooled bed.
Figure 1 is a flow sheet diagram of a preferred system for carrying out the process of the present invention.
Figure 2 is an electron microphotograph of an an hydrous alumina product made in accordance with the present invention.
A preferred fluid flash calcination system for carrying out the process of the invention is shown schematically in Figure 1.
alumina hydrate 8 from the Bayer process is filtered and washed with wash water 9 on a conventional table filter 10.
The filtered alumina hydrate at this stage comprises aluminum hydroxide, Allah. The filter product has both free moisture, to the extent of about 8-16 wit% HO, and chemically bound water amounting to about 34.6 wit% on dry Allah. As used herein, the term "residual water content" refers to the sum of free moisture and chemically bound water. For example, alumina containing 34.6 wit% chemically bound water and about 10 wit% free moisture has a residual water content of about 44.6 wit%.
The damp hydrate its fed into a flash dryer 20 through a feed screw 21. A gas line 22 feeds a hot gas stream into the dryer 20$ where tree water is driven off from the alumina hydrate. The dried hydrate is transferred to a first cyclone 30 where it is separated from hot gases and water vapor and discharged into a fluidized bed dryer 40. Hot gases and water vapor from the cyclone 30 are carried to an electrostatic precipitator 42 where dust is removed to a dust bin 43 and a clean off-gas is released to the atmosphere through a vent 44.
The dryer 40 contains alumina that is fluidized by air from an air source 46. The flash dryer 20, cyclone 30 and fluidized bed dryer 40 define, in combination, a dehydrating zone wherein the hydrate is heated to reduce its residual water content. ~eatecl alumina hydrate metered out of the dryer 40 through a valve 47 has a residual water content below about 15 wit%, usually below about 10 wit% and typically about 5 wit%. Off-gas released through the vent 40 contains steam originating from dehydration and calcination of the alumina as well as from steam used as a 1uidizlng gas.
The valve 47 releases hydrate at a controlled rate into a reactor or holding vessel 50. The reactor 50 includes a cyclone portion 51 and a lower portion 52 containing a fluidized bed of alumina. A steam source 53 fluidizes alumina in the reactor 50.
Hydrate released into the cyclone portion 51 contacts a hot gas stream which partially calcites the hydrate and carries it to a second cyclone 60. There, solids are separated from the hot gas and transferred into a furnace 70. Hot gas separated from the solids in the second cyclone 60 may conveniently be returned through a gas line 22 into the flash dryer 20.
In the furnace 70, fuel is burned in a series of peripherally located burners directly into a heating zone 71 containing a suspension of alumina. Residence time in the furnace 70 is short (about 10-100 seconds). The furnace 70 is preferably heated by combustion of natural gas at a flame temperature of about 16~9-1677C (3000-3500F). The furnace 70 may also be heated by combustion of other fossil fuels or by electric heater means. The furnace 70 heats alumina in the heating zone 71 to an elevated temperature above about 800C.
An alumina-gas suspension passes from the furnace 70 into the cyclone portion 51 of the reactor 50. Solid alumina particles separated in the cyclone portion 51 drop downwardly into the 1uidized bed in the lower portion 52.
Lo The fluidized bed is maintained at a temperature above about 900C, usually above about Luke, and preferably above about 1220C. An advantage of the present invention is the ability Jo maintain temperatures above about 1220C in the fluidized bed without losing control over temperature. Two particularly preferred operating temperatures in the reactor 50 are 1250C and 1275C.
A further advantage of the invention is that the reactor 50 does not require increased pressure. Reactor pressure is less than about 1.5 atmospheres, usually about atmospheric pressure or slightly higher.
Alumina is maintained in the fluidized bed reactor 50 for a sufficient time to transform it into an an hydrous alumina product comprising at least about 10 wit% alpha alumina.
Residence time in the reactor may be about 1 to 45 minutes, depending upon the temperature and desired alpha alumina content of the product. The reaction is usually maintained for a sufficient time to raise alpha alumina content to at least about 65 wit%, preferably at least about 80 wit%. The product may have surface area of less than about 10 mug usually less than about 5 mug or even less than about 3 mug Characteristics of the product can be controlled by varying retention time or reaction temperature.
The fl~lidizing gas introduced through the source 53 is principally steam. The fluidizing gas preferably comprises at least about 90 volume percent steam, and is optimally substantially all (greater than about 99 volume percent) s-team.
Usage of steam as the fluldizing gas permits operation of the reactor 50 at higher temperatures than might otherwise be s maintained for long periods of time and avoids collapse of the fluidized bed as a result of alumina particle stickiness at such temperatures. The steam may be superheated to a temperature above about 105C, usually not more than about 200C. The steam promotes crystal growth and enhances conversion to alpha alumina.
The exothermic reaction forming alpha alumina releases heat at a rate of about 133 BTU's per pound of alpha alumina formed. This heat of formation maintains alumina in the fluidized bed at an elevated operating temperature.
Hot alumina product is discharged through a valve Al and pneumatically conveyed through a series of cyclones I where the product is partially cooled. An air pump 81 supplies external air to the cyclones 80. Heated air may be returned from the cyclones 80 through an air duct 82 to the furnace 70 where such heated air provides a major portion of the air required for combustion. A small auxiliary burner 83 adjacent the air duct 82 ensures proper air temperature for combustion and also provides initial heating on start-up.
Alumina is discharged from the cyclones 80 into a two-bed fluidized cooler 90. The alumina is initially cooled with an air-cooled tubular heat exchanger 91 surrounding an upper bed. Air heated here can be transferred to the air source 46 for the fluidized bed dryer 40. Alumina cooled in the upper bed is dropped into a lower bed -for final cooling by a water-cooled heat exchanger 92. An air header 93 supplies air for fluidizing both beds in the cooler 90. The cooled alumina is shifted into a pneumatic conveyor 100 powered by an air source lo and then dumped into an alumina storage bin 110.
~3~6~ii Examples The preferred process described above results in an an hydrous alumina product having high alpha alumina content. A
typical product is shown in Figure 2, which is an electron microphotograph taken at OX magnification. This product was made by treating alumina with steam in the reactor 50 at a temperature of about 1275C. Alpha alumina content is about 85~, based upon intensity as measured by X-ray diffraction.
Surface area (BET) is about 2 mug The product is useful in ceramic and refractory applications calling for alumina having high alpha content. The product has superior grinding characteristics and is more uniform than alpha alumina products produced in a rotary kin.
Alumina heated at 1225C for 30 minutes in a vessel 50 containing a bed fluidized with steam resulted in a product having an alpha alumina content of about 87% and BET surface area of about 4 m go Alumina heated at 1270C for 13 minutes in a vessel 50 containing a bed flooded with steam resulted in a product with an alpha alumina content of about 88% and JET surface area of about 5 mug Various modifications may be made in the invention without departing from the spirit thereof, or the scope of the claims, and therefore, the exact form shown is to be taken as illustrative only and not in a limiting sense, and it is desired that only such limitations shall be placed thereon as are imposed by the prior art, or are specifically set forth in the appended claims.
Claims (16)
1. A process for transforming alumina hydrate into an anhydrous alumina product containing alpha alumina, said process comprising (a) heating alumina hydrate in a dehydrating zone to a sufficiently high temperature and for a sufficient time to obtain an alumina having a residual water content below about 15 wt%, (b) transferring the alumina from said dehydrating zone into a heating zone and there heating the alumina to an elevated temperature greater than the temperature in said dehydrating zone, (c) transferring the alumina from said heating zone into a reactor separate from said heating zone and there maintaining the alumina in a fluidized bed at a temperature of about 900-1350°C for a sufficient time to transform the alumina into an anhydrous alumina product comprising at least about 10 wt% alpha alumina, and (d) fluidizing the alumina in the reactor at a pressure of less than about 1.5 atmospheres with a fluidizing gas comprising principally steam.
2. The process of claim 1 wherein the residual water content of the alumina obtained in step (a) is below about 10 wt%.
3. The process of claim 1 wherein the alumina is heated in said heating zone to a temperature above about 800°C.
4. The process of claim 1 wherein the alumina is heated in said heating zone by combustion of natural gas.
5. The process of claim 4 wherein the flame temperature of said combustion is about 1649-1677°C,
6. The process of claim 1 wherein the alumina is maintained at a temperature of about 900-1350°C in said reactor.
7. The process of claim 1 wherein the alumina is maintained at a temperature above about 1100°C in said reactor.
8. The process of claim 1 wherein the alumina is maintained at a temperature above about 1220°C in said reactor.
9. The process of claim 1 wherein the alumina is maintained in said fluidized bed for a sufficient time to obtain a product comprising at least about 65 wt% alpha alumina.
10. The process of claim 1 wherein the alumina is maintained in said fluidized bed for a sufficient time to obtain a product comprising at least about 80 wt% alpha alumina.
11. The process of claim 1 wherein the alumina is maintained in said fluidized bed for a sufficient time to obtain a product having a surface area of less than about 10 m2/g.
12. The process of claim 1 wherein the alumina is maintained in said fluidized bed for a sufficient time to obtain a product having a surface area of less than about 6 m2/g.
13. The process of claim 1 wherein the alumina is maintained in said fluidized bed for a sufficient time to obtain a product having a surface area of less than about 3 m2/g.
14. The process of claim 1 wherein said fluidizing gas comprises at least about 90 volume percent steam.
15. The process of claim 1 wherein said fluidizing gas is substantially all steam.
16. A process for transforming alumina hydrate into an anhydrous alumina product containing alpha alumina, said process comprising (a) heating alumina hydrate in a dehydrating zone to a sufficiently high temperature and for sufficient time to obtain an alumina with residual water content below about 10 wt%, (b) transferring the alumina from said dehydrating zone into a heating zone and there heating the alumina to an elevated temperature greater than the temperature in said dehydrating zone, (c) transferring the alumina from said heating zone into a reactor separate from said heating zone and there maintaining the alumina in a fluidized bed at a temperature of about 1100-1300°C for a sufficient time to transform the alumina into an anhydrous alumina product comprising at least about 65 wt%
alpha alumina, and (d) fluidizing the alumina in the reactor at a pressure of less than about 1.5 atmospheres with a fluidizing gas comprising principally steam.
alpha alumina, and (d) fluidizing the alumina in the reactor at a pressure of less than about 1.5 atmospheres with a fluidizing gas comprising principally steam.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US06/719,559 US4585645A (en) | 1985-04-03 | 1985-04-03 | Alpha alumina production in a steam-fluidized reactor |
| US719,559 | 1985-04-03 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1236265A true CA1236265A (en) | 1988-05-10 |
Family
ID=24890516
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000496908A Expired CA1236265A (en) | 1985-04-03 | 1985-12-05 | .alpha. ALUMINA PRODUCTION IN A STEAM-FLUIDIZED REACTOR |
Country Status (10)
| Country | Link |
|---|---|
| US (1) | US4585645A (en) |
| JP (1) | JPS61232216A (en) |
| CN (1) | CN1006698B (en) |
| AU (1) | AU577908B2 (en) |
| BR (1) | BR8601483A (en) |
| CA (1) | CA1236265A (en) |
| DE (1) | DE3605525C2 (en) |
| ES (1) | ES8706573A1 (en) |
| FR (1) | FR2579971B1 (en) |
| IE (1) | IE60389B1 (en) |
Families Citing this family (22)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4847064A (en) * | 1987-12-23 | 1989-07-11 | Aluminum Company Of America | Economical process for alpha alumina production |
| US5225229A (en) * | 1986-07-18 | 1993-07-06 | Aluminum Company Of America | Aluminum hydroxide production |
| US5149520A (en) * | 1987-12-23 | 1992-09-22 | Aluminum Company Of America | Small sized alpha alumina particles and platelets |
| AU4316589A (en) * | 1988-09-30 | 1990-04-18 | Ferro Corporation | High surface area alpha-alumina and supercritical fluid synthesis thereof |
| DE69005643T2 (en) * | 1989-11-27 | 1994-05-19 | Alcan Int Ltd | METHOD FOR CALCINATING ALUMINUM OXIDE TRIHYDRATE FOR PRODUCING ALUMINUM OXIDE AND DEVICE THEREFOR. |
| DE4109743C2 (en) * | 1991-03-25 | 1995-03-23 | Escher Wyss Gmbh | Process for the thermal treatment of moist hydrates |
| DE19542309A1 (en) * | 1995-11-14 | 1997-05-15 | Metallgesellschaft Ag | Process for the production of aluminum oxide from aluminum hydroxide |
| US20050238571A1 (en) * | 2004-04-26 | 2005-10-27 | Raahauge Benny E | Process and apparatus for the production of alumina |
| CN1310968C (en) * | 2004-07-05 | 2007-04-18 | 中国石油化工股份有限公司 | Catalyst used for olefine polymerization or copolymerization, its preparation method and application |
| CN100406104C (en) * | 2005-01-26 | 2008-07-30 | 中国铝业股份有限公司 | Clinker dissolving out milled dust collecting method and washing tower thereof |
| CN100417671C (en) * | 2005-03-16 | 2008-09-10 | 中国石油化工股份有限公司 | Catalyst compsns. for olefin polymerization and catalyst thereof |
| US9650305B2 (en) * | 2007-12-28 | 2017-05-16 | United States Gypsum Company | Hard water foaming agents and methods for gypsum board production |
| CN103534367A (en) | 2011-03-18 | 2014-01-22 | 奥贝特铝业有限公司 | Processes for recovering rare earth elements from aluminum-bearing materials |
| AU2012250460B2 (en) | 2011-05-04 | 2015-11-26 | Orbite Aluminae Inc. | Processes for recovering rare earth elements from various ores |
| RU2014114938A (en) | 2011-09-16 | 2015-10-27 | Орбит Элюминэ Инк. | METHODS FOR PRODUCING ALUMINUM OXIDE AND VARIOUS OTHER PRODUCTS |
| CA2875776A1 (en) | 2012-01-10 | 2013-07-18 | Richard Boudreault | Processes for treating red mud |
| RU2633579C9 (en) | 2012-03-29 | 2017-12-25 | Орбит Алюминэ Инк. | Methods of treating fly ash |
| MY190290A (en) | 2012-07-12 | 2022-04-12 | Orbite Tech Inc | Processes for preparing titanium oxide and various other products |
| BR112015011049A2 (en) | 2012-11-14 | 2017-07-11 | Orbite Aluminae Inc | Methods for Purification of Aluminum Ions |
| US20170121182A1 (en) * | 2014-05-30 | 2017-05-04 | Orbite Technologies Inc. | Calcination processes for preparing various types of alumina |
| US20170260062A1 (en) * | 2014-10-03 | 2017-09-14 | Orbite Technologies Inc. | Methods for purifying aluminium ions |
| DE102015108722A1 (en) * | 2015-06-02 | 2016-12-08 | Outotec (Finland) Oy | Process and plant for the thermal treatment of granular solids |
Family Cites Families (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2642337A (en) * | 1948-06-09 | 1953-06-16 | Aluminum Co Of America | Method of converting crystalline alumina hydrate to alpha alumina |
| FR1248038A (en) * | 1959-10-28 | 1960-12-09 | Electrochimie Electrometallurg | Anhydrous aluminas manufacturing process |
| FR1295554A (en) * | 1961-04-28 | 1962-06-08 | Electrochimie Soc | Device for the production of anhydrous aluminas |
| US3442606A (en) * | 1967-02-07 | 1969-05-06 | Reynolds Metals Co | Removal of fluorine from alumina by steam |
| GB1143880A (en) * | 1967-06-16 | 1900-01-01 | ||
| US4224302A (en) * | 1975-09-16 | 1980-09-23 | Nippon Soken Inc. | Process for producing an alumina catalyst carrier |
| AU518907B2 (en) * | 1979-01-08 | 1981-10-29 | Monash University | Alumina production |
| CH654819A5 (en) * | 1980-09-23 | 1986-03-14 | Alusuisse | METHOD FOR PRODUCING COARSE CRYSTALLINE ALPHA ALUMINUM OXIDE AND THE USE THEREOF. |
| FR2562075B1 (en) * | 1984-03-29 | 1986-06-20 | Commissariat Energie Atomique | NOVEL URANIUM COMPOUNDS, PROCESS FOR THEIR PREPARATION AND THEIR USE AS CATALYSTS FOR HYDROGENATION OF UNSATURATED ORGANIC COMPOUNDS |
-
1985
- 1985-04-03 US US06/719,559 patent/US4585645A/en not_active Expired - Lifetime
- 1985-12-05 CA CA000496908A patent/CA1236265A/en not_active Expired
- 1985-12-13 AU AU51211/85A patent/AU577908B2/en not_active Ceased
-
1986
- 1986-02-20 DE DE3605525A patent/DE3605525C2/en not_active Expired - Fee Related
- 1986-03-13 FR FR868603567A patent/FR2579971B1/fr not_active Expired
- 1986-03-20 IE IE72486A patent/IE60389B1/en not_active IP Right Cessation
- 1986-03-28 JP JP61068863A patent/JPS61232216A/en active Granted
- 1986-04-02 CN CN86102252A patent/CN1006698B/en not_active Expired
- 1986-04-02 ES ES553655A patent/ES8706573A1/en not_active Expired
- 1986-04-02 BR BR8601483A patent/BR8601483A/en not_active IP Right Cessation
Also Published As
| Publication number | Publication date |
|---|---|
| CN1006698B (en) | 1990-02-07 |
| DE3605525A1 (en) | 1986-10-16 |
| BR8601483A (en) | 1986-12-09 |
| IE60389B1 (en) | 1994-07-13 |
| ES553655A0 (en) | 1987-06-16 |
| JPH0461812B2 (en) | 1992-10-02 |
| FR2579971A1 (en) | 1986-10-10 |
| DE3605525C2 (en) | 1995-02-23 |
| CN86102252A (en) | 1987-01-28 |
| FR2579971B1 (en) | 1989-09-08 |
| AU577908B2 (en) | 1988-10-06 |
| IE860724L (en) | 1986-10-03 |
| JPS61232216A (en) | 1986-10-16 |
| ES8706573A1 (en) | 1987-06-16 |
| AU5121185A (en) | 1986-10-09 |
| US4585645A (en) | 1986-04-29 |
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